System and method of selective adjustment of a color display

ABSTRACT

Some embodiments of the invention provide a method a device and/or a system for selective color adjustment including adjusting an intensity value of a first primary color component of a pixel based, at least in part, on an intensity value of a second primary color component of the pixel.

FIELD OF THE INVENTION

The invention relates generally to color adjustment of color displaysand, more particularly, to selective adjustment of a primary colorcomponent of the display.

BACKGROUND OF THE INVENTION

Liquid Crystal (LC) devices are used in different types of displays,including LC transmission-type displays for direct viewing, typicallyemployed by laptop and desktop computers, cellular telephones, and othermobile devices. In recent years, LC on silicon devices (LCoS) have beendeveloped for use as reflective or transmissive spatial light modulators(SLM's) of projection display devices. Such a projection display deviceincludes an array of LC cells, one or more cell for each image pixel,wherein each cell modulates the intensity of light passing through orreflected from the cell. The LC cell rotates the polarization of theincident polarized light according to the voltage applied to the cell.The outgoing light passes through an additional polarizing element.Therefore, the ratio between the intensity of outgoing light and that ofthe incident light is controlled by the rotation of the polarization.Generally, if the two fixed polarizers are set in perpendicularpolarizations and the LC cell does not rotate the polarization of theincoming light, the device is in a “dark” state. Conversely, if the LCcell rotates the polarization by 90 degrees, the device is in a “bright”state. Partial rotation of the polarization yields intermediate tones,i.e., gray levels. The relation between the applied voltage and therelative intensity obtained from the device, with respect to the brightstate, is commonly referred to as the “response function” of the device,or the “gamma” of the device.

“Gamma correction” refers to a function applied to a LC device to adjustits tone gradation response. In a typical Gamma correction algorithm,pixel data is converted into new values using a look-up-table. The newvalues are used to control the voltage applied to the device. Using suchlook-up-table correction, the gradation response can be adjusted to meetrequired performance parameters.

In color displays, the light modulated by the SLM is also filtered byappropriate color filters. The combination of colored light andcontrolled gradation levels for each of a plurality of primary colorpixels allows the representation of color images. The mixing of thedifferent primaries may be temporal, as in sequential projectiondevices; simultaneous, as in three-panel RGB projection devices; orspatial, as in direct view LC display devices. In sequential displaysystems, a stream of sequential single color sub-frames is temporallyintegrated by the viewer's eye to obtain a color image. In simultaneousdisplay systems, three RGB sub-images, produced by three separatepanels, are viewed simultaneously. In direct view systems, the eye ofthe viewer integrates the light coming from neighboring sub-pixels ofdifferent colors to obtain a full color image.

An underlying assumption in the design of existing LC color displays isthat the color of outgoing light may be determined in a straightforwardmanner by the light source and color filters used. According to thisassumption, the chromaticity of a primary color pixel is determined bythe respective light source and/or color filter, and the intensity ofthe primary color pixel is determined by the amount of the polarizationrotation of the respective LC cell. Thus, according to the aboveassumption, the control of intensity is separated from the chromaticityof the primary. Unfortunately, while the above assumption is reasonablyaccurate in the case of cathode ray tube (CRT) color displays, it issignificantly inaccurate in the case of LC color displays. Nevertheless,this straightforward approach, which is inherently inaccurate,simplifies the handling of data for color images in existing LC colordisplays.

An inherent problem of LC devices is that they do not behave as perfectpolarization rotators. The polarization rotation depends on the width ofthe LC layer, the difference between the effective refractive indicesfor the two polarization modes, and the wavelength of incident light.For non-monochromatic light, the amount of polarization rotation willdepend on the wavelength and, therefore, the transmission of differentwavelengths in the spectra may differ significantly. Furthermore, theremay be significant differences in the relative transmission of differentwavelengths between the “bright” state and the “dark” state of the cell.Thus, changing the voltage applied to the cells affects the spectrum ofthe outgoing light in addition to its intensity and, therefore, theviewed colors may be significantly distorted. This inaccuracy is notdesirable in any color display, but may be particularly significant incolor display applications that require enhanced accuracy in viewingcolors, such as print-proofing or high-end display applications.

SUMMARY OF EMBODIMENTS OF THE INVENTION

According to exemplary embodiments of the invention, RGB data providedto a pixel of a display, e.g., a LCD based display, may be corrected oradjusted so that the color of the displayed pixel would be similar tothe color produced with the same RGB input data on a reference display.In this context, the reference display may be defined as a display withthe property that the chromaticity values of primary color pixelcomponents, and thus the colors of pixels, are independent of theintensity of the primary color pixel components, which determine theintensity of the pixels.

According to embodiments of the invention, a method of selective colordisplay adjustment may include adjusting an intensity value of a firstprimary color component of a pixel based, at least in part, on anintensity value of a second primary color component of the pixel, asdescribed in detail below.

According to embodiments of the invention the method may also includeperforming the adjusting for a plurality of pixels of a color image tobe displayed by the color display.

According to embodiments of the invention, the method may includecalculating an adjusted intensity value for the first primary colorcomponent using a conversion operator dependent on one or more of theintensity values of the primary color components.

According to some exemplary embodiment of the invention, the method mayinclude determining an initial conversion operator, and converting theintensity values of the primary color components into initial convertedintensity values using the initial conversion operator. The method mayalso include adjusting the conversion operator based on the convertedvalues to provide an adjusted conversion operator, and converting theintensity values of the primary components using the adjusted conversionto provide adjusted converted intensity values. The method may furtherinclude comparing between the initial converted intensity values and theadjusted converted intensity values, re-initializing the conversionoperator according to the adjusted conversion operator, and repeatingthe adjusting, the converting based on the adjusted conversion operator,and the re-initializing, until a predefined difference between theinitial converted intensity values and the adjusted converted intensityvalues is achieved.

According to other exemplary embodiments of the invention, the methodmay include obtaining one or more device-dependent intensity valuescorresponding to one or more imaginary intensity values of the primarycolor components, and combining one or more of the device dependentintensity values. The obtaining of one or more device-dependent valuesmay include using one or more look-up tables to associate each of theone or more imaginary intensity values with a respective plurality ofthe device-dependent values.

According to other exemplary embodiments of the invention, the methodmay include adding a sub-adjustment value to a first imaginary intensityvalue based on a second imaginary intensity value, wherein the first andsecond imaginary intensity values correspond to the first and secondprimary color components, respectively.

According to embodiments of the invention there is provided a displaysystem including a color adjustment unit to selectively adjust anintensity value of a first primary color component of a pixel based, atleast in part, on an intensity value of a second primary color componentof the pixel. The system may also include a driver to receive theadjusted intensity value from the color adjustment unit and to drive acolor display device according to the adjusted intensity value.

According to some exemplary embodiments, the color adjustment unit mayinclude a logic unit to obtain one or more device-dependent intensityvalues corresponding to one or more imaginary intensity values of theprimary color components, and to combine one or more of the devicedependent intensity values.

According to other exemplary embodiments, the color adjustment unit mayinclude a logic unit to add a sub-adjustment value to a first imaginaryintensity value based on a second imaginary intensity value, wherein thefirst and second imaginary intensity values correspond to the first andsecond primary color components, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood and appreciated more fully from thefollowing description of embodiments of the invention read inconjunction with the accompanying drawing, in which:

FIG. 1 is a schematic flow chart illustration of an iterative method ofselective color display adjustment in accordance with exemplaryembodiments of the invention;

FIG. 2 is a schematic chromaticity diagram, showing a color gamut thatmay be used to define imaginary primary colors in accordance withexemplary embodiments of the invention;

FIG. 3 is a schematic flow chart illustration of a non-iterative methodof selective color display adjustment in accordance with exemplaryembodiments of the invention;

FIG. 4 is a schematic flow chart illustration of a method of selectivecolor adjustment for a more than three primary color display, inaccordance with exemplary embodiments of the invention; and

FIG. 5 is a schematic block diagram illustration of a system ofselective color display adjustment in accordance with exemplaryembodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

According to exemplary embodiments of the invention, the RGB dataprovided to a pixel of a display, e.g., a LCD based display, may becorrected or adjusted so that the color of the displayed pixel would besimilar to the color produced with the same RGB input data on areference display. In this context, the reference display may be definedas a display with the property that the chromaticity values of primarycolor pixel components, and thus the colors of pixels, are independentof the intensity of the primary color pixel components, which determinesthe intensity of the pixels.

According to embodiments of the invention, a method of selective colordisplay adjustment may include adjusting an intensity value of a firstprimary color component of a pixel based, at least in part, on anintensity value of a second primary color component of the pixel, asdescribed in detail below.

A color of a given pixel of a reference display may be calculated byapplying elements of a matrix of primary color components to alinearized input of the pixel. To produce a linearized input,three-primary input data, e.g., RGB data, may be converted into a signalrepresenting linear intensity levels of the primary color components,whereby the color of the pixel may be determined in absolute terms,e.g., using a three dimensional coordinate system, for example, XYZcoordinates. Thus, the color of a pixel may be defined in terms of aweighted sum of the XYZ coordinates, wherein the relative weights ofdifferent primaries are determined by their respective linear intensityvalues. In mathematical terms, an XYZ color vector may be obtained, forexample, by multiplying an input RGB vector (also referred to as “RGBtriad”) by an appropriate matrix, as follows: $\begin{matrix}{\begin{pmatrix}X_{C} \\Y_{C} \\Z_{C}\end{pmatrix} = {\begin{pmatrix}X_{R} & X_{G} & X_{B} \\Y_{R} & Y_{G} & Y_{B} \\Z_{R} & Z_{G} & Z_{B}\end{pmatrix} \cdot \begin{pmatrix}R \\G \\B\end{pmatrix}}} & (1)\end{matrix}$

In Equation 1, the subscript “c” indicates the color corresponding tothe input RGB triad, and the subscripts “R”, “G” and “B” represent thecorresponding display primaries in this example. Thus, the conversionmatrix from RGB to XYZ may be based on the XYZ values of the displayprimaries. This matrix is referred to herein as the “direct conversionmatrix”. It should be noted that the triad (X_(C), Y_(C), Z_(C))represents the colorimetric value of the color of the pixel as itappears on a reference display characterized by the direct conversionmatrix, for linearized RGB signals. It will be appreciated by thoseskilled in the art that according to embodiments of the invention,Equation 1 may be implemented in various forms, for example, in thedirect conversion matrix form, to transform any first color data format,e.g., RGB data, into any second color data format, e.g., XYZ data. Forexample, the second color format may be based on any RGB space includingpre-defined luminance-independent red, green and blue primarycomponents.

Some applications may require conversion of the second color dataformat, e.g., the XYZ data or data in any other pre-defined absolutecolor coordinates, back into corresponding values in the first colordata format, e.g., the RGB data format or any other device-dependentprimary color data format. In general, such conversion may be requiredwhen it is desired to more accurately control the color appearing on thedisplay, namely, to control the values of a vector (X_(C), Y_(C),Z_(C)), e.g., in applications that cannot rely on the accuracy of thedevice-dependent colors produced in response to the original RGB data.Examples of display systems that require enhanced accuracy may includedisplay systems used in color print proofing applications, or LC displaysystems designed to emulate the color accuracy of CRT display systems.In such cases, the XYZ data may be based on a model of the behavior ofthe print or the CRT monitor, and conversion into RGB values or intoother desired primary-color formats may be required in order to obtainthe required XYZ response by the LC display. Alternatively, such aconversion may be done to avoid color shifts in the presentation ofvideo image that may affect the quality of the presented image.

It will be appreciated by those skilled in the art that according toembodiments of the invention, the RGB data format may be used forrepresenting the absolute color space as well as for representingadjusted color coordinates. For example, RGB input data may be convertedinto an absolute color space including “pure” primary color components,whose chromaticity values do not depend on the intensity values of thecomponents. An adjustment may be applied to the intensity values of theRGB data in the absolute color space such that when the adjusted valuesundergo a color shift by the display, the resulting color would be theone calculated for the absolute space. It will be noted, that althoughthe absolute color space may be represented in terms of the RGB colorspace, e.g., as described above, in the following description theabsolute color space will be referred to as the XYZ color space.

According to exemplary embodiments of the invention, the conversion fromthe XYZ values back into the RGB values may be performed by matrixmultiplication. For example, an inverted primary-color matrix may beused, as follows: $\begin{matrix}{\begin{pmatrix}R \\G \\B\end{pmatrix} = {\begin{pmatrix}X_{R} & X_{G} & X_{B} \\Y_{R} & Y_{G} & Y_{B} \\Z_{R} & Z_{G} & Z_{B}\end{pmatrix}^{- 1} \cdot \begin{pmatrix}X_{C} \\Y_{C} \\Z_{C}\end{pmatrix}}} & (2)\end{matrix}$

The inverted conversion matrix in Equation 2, hereinafter referred to asthe “inverse conversion matrix”, may be obtained by inverting the directconversion matrix.

The conversion in Equation 2 assumes that the chromaticity of thedisplay primaries is fixed, e.g., as in a CRT display, and that thechange in the relative intensity of the primary does not influence thedisplayed chromaticity. However, as discussed above, this is not thecase for LC displays, wherein the chromaticity of the primaries may varysignificantly with intensity. Thus, the use of a fixed inverseconversion matrix to convert from XYZ values into RGB values wouldresult in distortion of the colors displayed by the LC display.

According to embodiments of the invention, this problem may be solved byusing an inverse conversion matrix including elements, which aredependent on the intensity values of the primary color components. Thismay be achieved, for example, by mapping the XYZ values of each of theprimary colors as a function of its intensity, as described below.

According to embodiments of the invention, the intensity value of eachprimary color may be scaled to a value in the range of 0-1, wherein avalue of 1 indicates maximum intensity for that primary and a value of 0indicates minimum intensity. Using the maximum value as a reference, theintensity may be reduced by changing the input data to values smallerthan 1. For example, the coordinate R in the one-dimensional “red” spacemay be mapped to a vector R in the three dimensional XYZ space, using afunction R(R). Analogous mapping may be used for all the primary colors,e.g., to produce red and blue vectors, Gand B, respectively.

According to exemplary embodiments of the invention, when thechromaticity of the primary is fixed with respect to the intensity, thefollowing mapping may be used:R=R·, wherein r=(X_(R), Y_(R), Z_(R)) is a fixed vector;G=G·g, wherein g=(X_(G), Y_(G), Z_(G)) is a fixed vector; andB=B·b, wherein b=(X_(B), Y_(B), Z_(B)) is a fixed vector.  (3)

When the chromaticity of the primary is not fixed with respect to theintensity, the following mapping may be used:R=R·r(R), wherein r is a function of the coordinate RG=G·g(G), wherein g is a function of the coordinate GB=B·b(B), wherein b is a function of the coordinate B  (4)

According to some exemplary embodiments of the invention, for eachprimary, the corresponding vector function in Equation 4 may be replacedby a set of three look-up-tables (LUT's) including normalized X, Y and Zvalues of that primary as a function of the intensity of the primary,e.g., the function r(R) may be pre-sampled to map a plurality ofdiscrete R values into corresponding normalized vectors, the functiong(G) may be pre-sampled to map a plurality of discrete G values intocorresponding normalized vectors, and the function b(B) may bepre-sampled to map a plurality of discrete B values into correspondingnormalized vectors. Given the three functions r(R), g(G) and b(B),selective color adjustment in accordance with embodiments of theinvention may be applied as described below.

Reference is now made to FIG. 1, which schematically illustrates aniterative method of selective color display adjustment in accordancewith exemplary embodiments of the invention.

As indicated at block 102, the method may include determining an initialconversion operator corresponding to a conversion of XYZ values, i.e.,intensity values of the primary color components into initial convertedRGB values.

According to exemplary embodiments of the invention, determining theinitial conversion operator may include selecting one or more intensityvalues. For example, when an input XYZ_(C) enters the system,predetermined values of XYZ for each primary color, e.g., the brightestlevel values for r(R=1), g(G=1) and b(B=1), may be used to create adirect conversion matrix similar to the direct matrix of Equation 1. Thedirect matrix may then be inverted to obtain the conversion operator,which may include an inverse conversion matrix similar to the inverseconversion matrix of Equation 2.

As indicated at block 104, the method may also include converting theXYZ values into the initial converted intensity values, using theinitial conversion operator, i.e., using the inverse conversion matrix.

As indicated at block 106, the conversion operator may be adjusted basedon the converted values, i.e., the RGB values. This may be achieved, forexample, by using the RGB values as inputs for the primary colorfunctions r(R), g(G) and b(B), so that adjusted XYZ values for each ofthe primaries are obtained, as indicated at block 108. According to someexemplary embodiments a set of LUTs may be used, each LUT may includethe adjusted XYZ values corresponding to one of the primaries. Theadjusted XYZ values may be used to create an adjusted direct conversionmatrix, as indicated at block 109. An adjusted inverse conversion matrixmay be constructed by inverting the adjusted direct conversion matrix,as indicated at block 110.

As indicated at block 111, the input XYZ values may be converted usingthe adjusted conversion operator to provide adjusted converted intensityvalues. For example, the adjusted conversion operator, i.e., theadjusted inverse conversion matrix, may be multiplied by the input data,e.g., according to Equation 2, to obtain an adjusted set of RGB values.

As indicated at block 112, the method may also include comparing betweenthe initial converted intensity values and the adjusted convertedintensity values.

As indicated at block 114, the conversion operator may bere-initialized. For example, the conversion operator may bere-initialized according to the values of the adjusted conversionoperator. This may be achieved, for example, by substituting elements ofthe initial conversion operator with respective values of the adjustedconversion operator.

As shown in FIG. 1, according to exemplary embodiments of the invention,the above process, may be repeated, iteratively, until the differencebetween consecutive iterations is sufficiently small, i.e., until apre-determined difference between the initial converted intensity valuesand the adjusted converted initial values is achieved. However, itshould be appreciated that in many cases a single iteration may besufficient to reach the desired color accuracy. Furthermore, sinceneighboring pixels of an image are typically similar, except in borderregions that cover only a small area of the image, there is generally noneed to start the process with the brightest level matrix for eachpixel; instead, the starting point for correcting the color of eachpixel may be based on the last matrix obtained for the previous pixel,i.e., the initial intensity values may be selected according tointensity values of primary color components of a neighboring pixel.This may result in a significantly more efficient iterative process,i.e., a smaller number of iterations may be required to determine thecorrect color of at least some of the pixels.

It is appreciated that, in certain applications, the iterative processdescribed above may not be sufficiently efficient. For example, theaccuracy that may be obtained by such an iterative process may belimited due to the speed required by motion video applications.Therefore, an aspect of the present invention avoids such iterativeprocedure, as described below.

As discussed above, the chromaticity of the primary colors may vary withtheir intensity, namely, each primary color may be represented by acurve on a chromaticity plane, such as the chromaticity diagram depictedin FIG. 2.

The dashed triangular area in FIG. 2 represents the color gamut that maybe obtained from combinations of three primary colors at an intensitylevel that results in the widest possible gamut that is fully containedby the color gamut obtained from the same primary colors at any otherintensity level. The corners of the triangular area, as defined above,define three chromaticity value points, which are referred to herein as“imaginary primary colors”. It will be appreciated by persons skilled inthe art that such imaginary primary colors may be pre-defined based ondevice-dependent color-shift parameters.

For a given intensity level of each imaginary primary, as defined above,it is possible to calculate the RGB values that would yield a correctchromaticity. For example, in case of the imaginary “red” primary, afunction r*(R*) defining a vector in the RGB space may be used, whereinR* denotes the intensity of the imaginary “red” primary and r* is athree-component vector of RGB values, the combination of which wouldyield a color with the chromaticity of the required imaginary redprimary at a normalized intensity R*. In this example, the chromaticityof the imaginary “red” primary is fixed, and R* is in the range of 0-1,wherein 1 represents the maximum intensity of the imaginary red primary.It should be noted that a fixed vector r*=(R, G, B), in which the valueof R is close to 1 and the values B and G represents small corrections,may be suitable for many types of display devices. It should beappreciated that the imaginary B and G primary colors may be defines byfunctions analogous to those used to define the imaginary R primary.

In some embodiments of the invention, the vector functions may beobtained using an iterative method, e.g., as described above withreference to FIG. 1; however other methods may also be suitable. Foreach imaginary primary, the RGB values of the vector functions may bestored in look-up-tables (LUTs), for example, three LUTs representing R,G and B, respectively, as described above.

Reference is now made to FIG. 3, which schematically illustrates a flowchart of a non-iterative method of selective color display adjustment,in accordance with exemplary embodiments of the invention.

As shown in FIG. 3, the received XYZ_(C) data signal or any other RGBdata with absolute reference primaries, as described above, may berepresented in terms of the set of imaginary primary colors.

As indicated at block 302, according to some exemplary embodiments ofthe invention, a conversion operator, e.g., an inverse matrix similar tothe inverse matrix of Equation 2, may be applied to the input intensityvalues of the primary components to obtain the corresponding imaginaryintensity values. Since the chromaticity of each imaginary primarycolor, e.g. the chromaticity of each imaginary primary color in thechromaticity diagram of FIG. 2, is independent of intensity, the inversematrix format of Equation 2 above may be used to obtain the relativeintensities of the imaginary primaries in a straightforward manner,namely from the input data the values R*, G* and B* may be calculated.

According to other exemplary embodiments of the invention, if theabsolute color is represented in terms of RGB space with a pre-definedset of fixed primaries, it may be useful to set the imaginary primariesto the values of the reference primaries. Thus, according to theseembodiments, conversion of the input data into corresponding imaginaryprimary intensities, e.g., as indicated by block 302, may not berequired.

As indicated at block 304, the method may include obtainingdevice-dependent intensity values corresponding to the imaginaryintensity values, e.g., the relative intensities R*, G*, B* may be usedto obtain the corresponding RGB values for each imaginary primary at thecorrect intensity level for that imaginary primary. For example a set ofLUTs, each including a set of device-dependent intensity valuescorresponding to one of the imaginary intensity values, may be used. Forexample, a LUT corresponding to values of R* may include sets of devicedependent intensity values R(R*), G(R*), and B(R*) such that a redimaginary primary at an intensity level R* may be produced by thedisplay device as a combination of R(R*), G(R*), and B(R*). Accordingly,a LUT corresponding to values of G* may include sets of device dependentvalues R(G*), G(G*), and B(G*), and a LUT corresponding to values of B*may include sets of device dependent values R(B*), G(B*), and B(B*).According to some exemplary embodiments, the device-dependent values ofthe LUTs may be calculated off-line using the iterative method describedabove with reference to FIG. 1.

As indicated at block 306, the method may also include combining thedevice-dependent values, e.g., based on the primary color components.Combining the device-dependent values may include calculating a sum ofthe device-dependent values corresponding to each of the imaginaryprimaries. For example, in order to create the required R* value of theimaginary red primary, the corresponding combination, e.g., the sum, ofthe R, G and B signal values found in the R* LUT may be sent to thedisplay. The same applies for the green and the blue imaginaryprimaries. Accordingly, the “R” signal sent to the display may bedetermined based on the sum of the R signals for the different imaginaryprimaries. Similarly, the B and G signals sent to the display may bedetermined based on the some of the different G and B signal components.

Since the display system may not be linear, the summation over the R, Gand B signals, as described above, may cause a slight shift in thechromaticity of the actual primary colors reproduced by the display.However, it will be appreciated by persons skilled in the art that thisshift would be negligible because, for example, the relativecontribution of the imaginary G and B components in determining the Rsignal are typically small and do not significantly affect the over-allintensity of the primary. Similarly, the intensity levels of G and B arenot significantly influenced by the additional, smaller, componentscontributing to their chromaticity correction.

Although the above methods are described in the context of three-primarycolor display systems, it will be appreciated by those skilled in theart that these methods are equally suitable for displays using four ormore primary colors. For example, in a more-than-three-primary system,the color shift of each primary as a function of its intensity may berecorded as described above. Additionally, more than three imaginaryprimary colors may be defined by the corners of a more-than-three-sidedshape of the gamut resulting from combinations of the real primaries ata certain intensity level, in analogy to the triangular gamut describedabove with reference to FIG. 2. Each such imaginary primary may have afixed chromaticity, as described above, and thus the conversion of inputcolors to imaginary primaries may be readily determined usingcalculations analogous to those demonstrated above and/or as describedin prior art publications relating to more-than-three primary displays.As described above, for each imaginary primary, off-line calculation maybe used to determine the combination of device-dependent primaries thatmay provide a pre-defined set of intensity values of the imaginaryprimary. Similarly, as in the three-primary system, for each colorinput, the combination of imaginary primaries that yields that color maybe calculated by analogous methods. Thus, the value of each imaginaryprimary at a given intensity level may be replaced by the pre-calculatedset of device-dependent primaries that reproduce the imaginary primaryat the correct intensity level and chromaticity.

In the above description, each of the imaginary primaries is describedin terms of combinations of all primaries to yield the chromaticity ofthe imaginary primary at different intensity levels. In practice,according to some exemplary embodiments of the invention, thecalculations described above may be simplified for a more-than threeprimary color display. In a more than three primaries display, the red,green and blue primaries may have a narrow spectral range and thus theircolor shift with intensity may be relatively small. Additionalprimaries, e.g., cyan and yellow, may have a relatively wide spectralrange and thus may suffer from large color shifts. Thus, according tosome embodiments of the invention, it may be required to adjustintensity values corresponding to only some of the primary components.Furthermore, in many cases the selective color adjustment may beachieved by adding only one primary to the adjusted primary component,as described below.

According to some exemplary embodiment, a shift in the yellow primarymay tend to be mostly on the red-green axis. If the imaginary yellowprimary were chosen to be on the red edge of the yellow color shift,then when the intensity is changed the yellow primary would “drift”towards the green primary. In order to adjust such a drift, theintensity of the red primary may be increased, and at the same time anintensity value of the yellow primary may be reduced, in order to keepthe displayed intensity at the required level. Thus, a fixedchromaticity yellow imaginary primary may be created by a combination ofonly two primaries, e.g., red and yellow. However, it will beappreciated by those skilled in the art that the adjustment may beanalogously achieved by a combination of green and yellow if theimaginary primary is chosen to be on the green side of the yellow colorshift. In a similar manner, a color shift of the cyan primary may beadjusted by one primary, e.g., green or blue. It will be appreciated bythose skilled in the art that in other embodiments of the invention, theuse of three, i.e. a selected primary to be adjusted and two primarieson both sides of the selected primary, may be required to adjust thecolor shift of the selected primary.

Thus, according to some embodiments of the invention, the non-iterativemethod for selective color adjustment, e.g., as described with referenceto FIG. 3, may be simplified, as described below.

Reference is made to FIG. 4, which schematically illustrates a flowchart of a method of selective color adjustment for a more than threeprimary color display, in accordance with exemplary embodiments of theinvention.

The following description may refer, for simplicity, to two categoriesof primary components, namely, major-shifted primary components andminor-shifted primary component. A major-shifted primary color maycorrespond to a primary component, e.g., yellow, which may have arelatively large color shift. A minor-shifted primary component maycorrespond to a primary component, e.g., red, which may be adjustedbased on an adjustment of a major-shifted primary component. However, itwill be appreciated by those skilled in the art that this categorizationis for simplicity only, and that according to other embodiments of theinvention the primary components may be categorized differently.

As indicated at block 402, the method may include receiving theimaginary primary values. The imaginary primary values may include atleast one major-shifted imaginary primary component and at least oneminor-shifted imaginary primary component.

As indicated at block 404, an adjusted major-shifted primary componentvalue may be obtained based on the major-shifted imaginary primarycomponent value. This may be achieved, for example, using a LUTincluding values of the adjusted major-shifted primary componentcorresponding to the values of the imaginary major-shifted primarycomponent, e.g., as described above.

As indicated at block 406, for one or more minor-shifted imaginaryprimary colors, e.g., a red imaginary primary value, a sub-adjustmentmay be performed, for example, using a LUT including sub-adjustmentvalues for the minor-shifted imaginary primary color, e.g., red,corresponding to the values of the major-shifted imaginary primarycolor, e.g. yellow, as described above.

As indicated at block 408, the sub-adjustment value may be added, forexample, to the value of the imaginary minor-shifted primary. Thus, amajor-shifted primary color signal sent to the display may include theadjusted major-shifted primary color value, and the sub-adjustment valuemay be added to the imaginary minor-shifted primary value to create aminor-shifted primary signal sent to the display. It may be noted that,for simplicity of description, it is assumed that the minor-shiftedprimary color does not have an adjustment or correction scheme, i.e.,the imaginary minor-shifted primary is similar in behavior to the “real”minor-shifted primary. It will be appreciated by persons skilled in theart that an adjustment scheme according to embodiments of the inventionmay also be applied to minor-shifted primary colors. In particular, aself-correction LUT on the value of the minor-shifted primary may beimplemented.

Although the raw color inputs used by embodiments of the invention havebeen described above in terms of XYZ data, it should be appreciated thatany other device-independent color representation may be used inconjunction with the present invention. Furthermore, device-dependedcolor representation, such as RGB or YCbCr, or any other suitableformats, may be appropriately defined as “device-independent” colors, inthe context of absolute color coordinates, such as the color coordinatesof CRT phosphors. Therefore, the use of XYZ in describing the exemplaryembodiments above should in no be interpreted to limit the scope of thepresent invention.

Reference is made to FIG. 5, which schematically illustrates a blockdiagram of a system 500 of selective color display adjustment inaccordance with exemplary embodiments.

According to exemplary embodiments of the invention, system 500 mayimplement principles of embodiments of the selective color adjustmentmethods described above.

According to embodiments of the invention, system 500 may include acolor adjustment unit 501 to selectively adjust an intensity value of afirst primary color component of a pixel based, at least in part, on anintensity value of a second primary color component of the pixel. Unit501 may include a logic unit 505 to receive unadjusted input data, andto produce an adjusted signal, e.g., a signal representing adjusted RGBcolor values, or adjusted color values in any other format of three ormore primary colors, as discussed above, suitable for driving a colordisplay device 503. The adjusted signal may be received by a driver 502,which drives the display device 503. Logic unit 505 may executealgorithms corresponding to any of the selective color adjustmentmethods described above. At least part of the function of logic unit 505may be implemented by any combination of software and/or hardware. Forexample, logic unit 505 may include a CPU, DSP, FPGA, ASIC, or any othertype of logic unit known in the art. Additionally or alternatively, partof the function of unit 505 may be implemented by means of a softwaredriver and/or as a “plug-in” to an existing software driver. Accordingto some exemplary embodiments, logic unit 505 may include one or morememory units 507 adapted to store one or more LUTs, e.g., as describedabove. For example, memory unit 507 may include a Random Access Memory(RAM), as is known in the art.

The present invention may be implemented in conjunction with any colordisplay system known in the art. Further, any type of display system ordevice incorporating elements of the methods, systems device describedabove in combination with other known elements, is also included withinthe scope of the present invention. Although some embodiments of thepresent invention may be particularly suitable for display systems usingLC devices, for example, direct-viewing displays, and sequential orsimultaneous projection displays, it should be appreciated that otherthe invention may also be used in conjunction with any other type ofdisplay system.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

1. A method of selectively adjusting colors displayed by a colordisplay, the method comprising adjusting an intensity value of a firstprimary color component of a pixel based, at least in part, on anintensity value of a second primary color component of said pixel. 2.The method of claim 1, wherein said pixel comprises three or moreprimary color components.
 3. The method of claim 2, wherein saidadjusting comprises adjusting the intensity value of said primary colorcomponent based on intensity values of all said three primary colorcomponents.
 4. The method of claim 2, wherein said three or more primarycolor components comprise four or more primary color components.
 5. Themethod of claim 4, wherein said adjusting comprises adjusting theintensity value of said first primary color component based on intensityvalues of one or more of said four or more primary color components. 6.A method according to claim 1 comprising performing said adjusting for aplurality of pixels of a color image to be displayed by said colordisplay.
 7. The method of claim 1, wherein said adjusting comprisescalculating an adjusted intensity value for said first primary colorcomponent using a conversion operator dependent on one or more of theintensity values of the primary color components.
 8. The method of claim7, wherein said conversion operator comprises a conversion inversematrix to convert the intensity values of said primary color componentsin an absolute data format into corresponding values in adevice-dependent data format.
 9. The method of claim 8, wherein one ormore elements of said conversion inverse matrix are dependent on one ormore of the intensity values of said primary color components.
 10. Themethod of claim 8, wherein said conversion inverse matrix corresponds toan inverse of a direct conversion matrix.
 11. The method of claim 10,wherein said direct conversion matrix comprises elements dependent onthe intensity values of said primary color components.
 12. The method ofclaim 7, wherein said adjusting comprising: determining an initialconversion operator; and converting the intensity values of said primarycolor components into initial converted intensity values using saidinitial conversion operator.
 13. The method of claim 12, whereindetermining said initial conversion operator comprises selecting one ormore initial intensity values.
 14. The method of claim 13 wherein saidinitial intensity values are selected according to intensity values ofprimary color components of a neighbor pixel adjacent to said pixel. 15.The method of claim 12 comprising: adjusting said conversion operatorbased on said converted values to provide an adjusted conversionoperator; and converting the intensity values of said primary componentsusing said adjusted conversion to provide adjusted converted intensityvalues.
 16. The method of claim 15, wherein adjusting said conversionoperator comprises: calculating elements of an adjusted directconversion matrix based on said converted values; and constructing aninverse matrix by inverting said adjusted direct conversion matrix. 17.The method of claim 16 wherein said calculating comprises: using one ormore look up tables to associate each of said converted values with aset of device dependent XYZ values; and constructing said adjusteddirect conversion matrix using said XYZ values.
 18. The method of claim15 comprising comparing between said initial converted intensity valuesand said adjusted converted intensity values.
 19. The method of claim 18comprising re-initializing said conversion operator according to saidadjusted conversion operator.
 20. The method of claim 19, whereinre-initializing said conversion operator comprises substituting elementsof said initial conversion operator with respective values of saidadjusted conversion operator.
 21. The method of claim 19 comprisingrepeating said adjusting, said converting based on said adjustedconversion operator, and said re-initializing, until a pre-determineddifference between said initial converted intensity values and saidadjusted converted intensity values is achieved.
 22. The method of claim1 wherein said adjusting comprises: obtaining one or moredevice-dependent intensity values corresponding to one or more imaginaryintensity values of said primary color components; and combining one ormore of said device dependent intensity values.
 23. The method of claim22, wherein said imaginary intensity values comprise the intensityvalues of said primary color components.
 24. The method of claim 22comprising obtaining said imaginary intensity values by applying apredefined conversion operator to input intensity values of said primarycolor components.
 25. The method of claim 22, wherein obtaining one ormore device-dependent values comprises using one or more look up tablesto associate each of said one or more imaginary intensity values with arespective plurality of said device-dependent values.
 26. The method ofclaim 22, wherein each of said device dependent values correspond to oneof said primary color components.
 27. The method of claim 26, whereinsaid combining comprises combining said device-dependent values based onsaid primary color components.
 28. The method of claim 27 wherein saidcombining comprises calculating a sum of the device dependent valuescorresponding to each of said primary color components.
 29. The methodof claim 1 comprising: adding a sub-adjustment value to a firstimaginary intensity value based on a second imaginary intensity value,said first and second imaginary intensity values corresponding to saidfirst and second primary color components, respectively.
 30. The methodof claim 29, wherein said imaginary intensity values comprise theintensity values of said primary color components.
 31. The method ofclaim 29 comprising obtaining said imaginary intensity values byapplying a predefined conversion operator to input intensity values ofsaid primary color components.
 32. A display system comprising: a coloradjustment unit to selectively adjust an intensity value of a firstprimary color component of a pixel based, at least in part, on anintensity value of a second primary color component of said pixel. 33.The system of claim 32 comprising a driver to receive said adjustedintensity value from said color adjustment unit and to drive a colordisplay device according to said adjusted intensity value.
 34. Thesystem of claim 32, wherein said color adjustment unit comprises a logicunit to obtain one or more device-dependent intensity valuescorresponding to one or more imaginary intensity values of said primarycolor components, and to combine one or more of said device dependentintensity values.
 35. The system of claim 34, wherein said imaginaryintensity values comprise the intensity values of said primary colorcomponents.
 36. The system of claim 34, wherein said logic unit isadapted to obtain said imaginary intensity values by applying apredefined conversion operator to input intensity values of said primarycolor components.
 37. The system of claim 34, wherein said logic unitcomprises one or more memory units to store one or more look up tablesto associate each of said one or more imaginary intensity values with arespective plurality of said device-dependent values.
 38. The system ofclaim 32, wherein said color adjustment unit comprises a logic unit toadd a sub-adjustment value to a first imaginary intensity value based ona second imaginary intensity value, said first and second imaginaryintensity values corresponding to said first and second primary colorcomponents, respectively.
 39. The system of claim 38, wherein saidimaginary intensity values comprise the intensity values of said primarycolor components.
 40. The system of claim 38, wherein said logic unit isadapted to apply a predefined conversion operator to input intensityvalues of said primary color components to obtain said imaginaryintensity values.
 41. The system of claim 38, wherein said logic unitcomprises a first memory unit to store a first look up table toassociate said sub-adjustment value with said second imaginary intensityvalue.